Mobile station capable of and a method for generating chip patterns for transmission

ABSTRACT

A mobile station that wirelessly transmits to a base station by DS-CDMA a signal spread by multiplying a spreading code includes a chip-pattern generating unit that generates a predetermined chip pattern by performing chip repetition for a predetermined number of repetitions to a spreading chip sequence, and a multiplying unit that multiplies to a signal including the predetermined chip pattern generated by the generating unit a phase specific to the mobile station.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a technology for wirelesstransmission, and particularly relates to a mobile station, a basestation, and a program for and a method of wireless transmission.

2. Description of the Related Art

The development of a fourth-generation mobile communications method,which is the next-generation mobile communications method beyondIMT-2000 (International Mobile Telecommunications-2000), has beenunderway. A fourth-generation mobile communications method flexiblysupporting a multi-cell environment including a cellular system, as wellas an isolated cell environment such as a hot-spot area and an indoorenvironment so as to seek a further increase in spectral usageefficiency at the respective cell environments, is being desired.

As a candidate wireless access method in the fourth-generation mobilecommunications which is applied to a link from a mobile station to abase station (referred to as an uplink below), DS-CDMA (DirectSequence-Code Division Multiple Access) is considered to be promisingfrom the point of view that it is particularly suitable for the cellularsystem. DS-CDMA multiplies to a transmitting signal a spreading code soas to spread to a wideband signal for transmission (refer tobelow-identified Non-Patent Document 1, for example).

Reasons that DS-CDMA is suitable for the multi-cell environmentincluding the cellular system are described below.

First, a suppression of the peak-to-average power ratio to a low levelrelative to a wireless access method using a large number ofsub-carriers such as OFDM (Orthogonal Frequency Division Multiplexing)and MC-CDMA (Multi-Carrier-Code Division Multiple Access) is enabled.Therefore, it is easy to implement a reduced power consumption which isone of the important desired conditions for the mobile station.

Second, while there is potential for a reduction in a requiredtransmitting power by a coherent-detection using dedicated pilotchannels, assuming that power levels of the pilot channels are the same,DS-CDMA relative to such methods as OFDM and MC-CDMA has a largerpilot-channel power per carrier. Therefore, an accurate channelestimation so as to suppress the required transmitting power to a lowlevel is enabled.

Third, in the multi-cell environment, even when using carriers havingthe same frequency in neighboring cells, DS-CDMA enables a suppressionin interference from the neighboring cells (referred to as “other-cellinterference” below) due to a spreading gain obtained by spreading.Therefore, an easy implementation of one-cell frequency reuse whichallocates all available spectral bands to the respective cells isenabled. Therefore, relative to TDMA (Time Division Multiple Access)which divides all available spectral bands so as to allocate differentspectral bands to the respective cells, an increase in the spectralusage efficiency is enabled.

However, as DS-CDMA is a wireless access method suitable in themulti-cell environment, there is a problem as described below as a causefor concern. In other words, in the isolated cell environment such asthe hot spot area and the indoor environment in which an effect ofother-cell interference is usually small, the advantage of reducingother-cell interference by spreading is low. Therefore, in DS-CDMA, alarge number of signals of simultaneously accessing mobile stations needto be accommodated in order to achieve the same level of spectral usageefficiency as in TDMA.

For example, when the respective mobile stations transmit transmittingsignals having multiplied spreading codes with spreading factor of SF,the transmission data rate becomes 1/SF so that with DS-CDMA there is aneed to accommodate the signals from SF mobile stations in order toachieve the same level of spectral usage efficiency as TDMA. However, inan actual uplink wireless propagation environment, an effect ofMultiple-Access Interference (MAI) in which the signals from therespective mobile stations interfere with one another due to differencesin condition of propagation from the respective mobile stations to thebase station (for instance, propagation delay time, change ofpropagation channel) becomes predominant. As a result, the spectralusage efficiency normalized by the spreading factor as described aboveis reduced to about 20-30 percent.

On the other hand, IFDMA (Interleaved Frequency Division MultipleAccess) is being studied as a wireless access method which enables areduction of the MAI as described above (for example, refer tobelow-identified Non-Patent Document 2). IFDMA applies a symbolrepetition to a data symbol so as to perform a sorting to generate apredetermined symbol pattern and to multiply a mobile station-specificphase to a transmitting signal for transmission. IFDMA reduces the MAIas the generation of the predetermined symbol pattern and themultiplying of the mobile station-specific phase set the signals fromthe respective mobile station to be arranged on the frequency axiswithout overlapping one another.

Furthermore, a study of a transmission timing control as another methodof reducing such MAI so as to improve the spectral usage efficiency isunderway (for example, refer to below-identified Non-Patent Document 3).FIG. 43A and FIG. 43B are diagrams which respectively illustrate timecharts for a case of applying a transmission timing control in an uplinkand for a case of not applying such control according to the relatedart. As illustrated in the case of FIG. 43A in which a transmissiontiming control is not applied, the signals transmitted from therespective receivers 200 through 220 have non-coincident receivedtimings at the base station 100 due to the different delay times ofpropagation to the base station 100. Therefore, with the transmissiontiming control, the transmitting timings of the respective mobilestations 200 through 220 are controlled so that the respective signalstransmitted from the respective mobile stations 200 through 220 arereceived at the same timing at the base station 100. Such performing oftransmission timing control enables reception of signals at the basestation 100 from the respective mobile stations 200 through 220 at thesame time (refer to FIG. 43B). When using at this time orthogonal codeas spreading code, the received signals from the different respectivemobile stations at such timing are orthogonal to one another so as toreduce the MAI. Hereby, improvement in the spectral usage efficiency isenabled.

Furthermore, a study of a technology which suppresses, for a receivedsignal affected by multi-path interference, multi-path interference bysignal processing at the receiver is underway. A multi-path interferencecanceller (for example, refer to below-identified Non-Patent Document 4)as illustrated in FIG. 44, a chip equalizer (for example, refer tobelow-identified Non-Patent Document 5) as illustrated in FIG. 45, and afrequency-domain equalizer (for example, refer to below-identifiedNon-Patent Document 6) as illustrated in FIG. 46 are representativeexamples.

The multi-path interference canceller as illustrated in FIG. 44estimates and generates at a multi-path interference signal estimator351 a signal component causing multi-path interference (referred to as amulti-path replica below) and subtracts the estimated multi-pathinterference replica as described above from a received signal. Hereby,a, reproduction of a received signal having a reduced multi-pathinterference effect is enabled.

The chip equalizer as illustrated in FIG. 45 generates at achannel-matrix generator 361 a channel matrix which shows the amount ofchange through a propagation channel of a received signal so as toderive from the matrix at a weighting factor estimator 362 a weightingfactor which reduces multi-path interference from the matrix and tomultiply at the chip equalizer 363 the weighting factor as describedabove and the received signal (this operation is referred to as an chipequalization). Hereby, a reduction of an effect of multi-pathinterference is enabled.

The frequency-domain equalizer as illustrated in FIG. 46 converts areceived signal at a time-to-frequency converter 371 into afrequency-domain signal so as to then derive at a weighting-factorestimator 372 a weighting factor which reduces multi-path interference,and to multiply at the frequency-domain equalizer 373 a weighting factorto the received frequency-domain signal so as to convert to the timedomain at the frequency-to-time converter 374. The performing of suchoperations enables a reducing of the effect of multi-path interference.

Non-Patent Document 1

H. Atarashi, S. Abeta, and M. Sawahashi, “Broadband packet wirelessaccess appropriate for high-speed and high-capacity throughput,” IEEEVTC2001-Spring, pp. 566-570, May 2001

Non-Patent Document 2

M. Schnell, I. Broek, and U. Sorger, “A promising new widebandmultiple-access scheme for future mobile communication systems,”European Trans. on Telecommun. (ETT), Vol. 10, No. 4, pp. 417-427,July/August 1999

Non-Patent Document 3

Een-Kee Hong, Seung-Hoon Hwang, and Keum-Chan Whang, “Synchronoustransmission technique for the reverse link in DS-CDMA terrestrialmobile systems,” pp. 1632-1635, Vol. 46, No. 11, IEEE Trans. on Commun.,November, 1999

Non-Patent Document 4

Kenichi Higuchi, Akihiro Fujimura, and Mamoru Sawahashi, “Multi-pathInterference Canceller for High-Speed Packet Transmission With AdaptiveModulation and Coding Scheme in W-CDMA Forward Link,” IEEE Selected AreaCommunications, Vol. 20, No. 2, February 2002

Non-Patent Document 5

A. Klein, “Data detection algorithms specially designed for the downlinkof CDMA mobile radio systems”, in Proc. IEEE VTC'97, pp. 203-207, May1997

Non-Patent Document 6

D. Falconer, S L Ariyavisitakul, A. Benyamin-Seeyar, and B. Eidson,“Frequency domain equalization for single-carrier broadband wirelesssystems”, IEEE Commun. Mag., Vol. 40, No. 4, pp. 58-66, April 2002.

However, because there is no spreading gain in IFDMA, it is necessary todivide all available spectral bands so as to allocate different spectralbands to the respective cells. Therefore, even when adopting suchwireless access method, it is difficult to seek an increase in thespectral usage efficiency in both the multi-cell environment and theisolated cell environment. The increase in the spectral usage efficiencyincreases the number of mobile stations which can be accommodated in thebase station at the respective cells so as to achieve an increasedcommunications-link capacity.

Furthermore, as the related-art technologies as described above aretechnologies concerning single elements within a wireless transmissionsystem, in order to actually build a wireless transmission system, astudy on a specific configuration of a base station and a mobile stationas well as on an overall configuration and also on a specificcontrolling method of these single-element technologies is needed.

However, as a sufficient study concerning the points as described abovehas not been performed to date, there is a demand for a specificconfiguration of a base station and a mobile station.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a wirelesstransmission, a mobile station, a base station, a program for, and amethod of a wireless transmission that substantially obviate one or moreproblems caused by the limitations and disadvantages of the related art.

In light of the problems as described above, it is a more particularobject of the present invention to provide a mobile station, a basestation, a program for and a method of a wireless transmission thatachieves an increased capacity of a communications link in both cellenvironments as described above for conducting communications byDS-CDMA. Furthermore, the present invention relates to a mobile station,a base station, a program for, and a method of a wireless transmissionwhich achieves improvement in the spectral usage efficiency, forexample, in an isolated cell environment as the increased capacity isachieved by one-cell reuse.

According to the invention, a mobile station which wirelessly transmitsto a base station by DS-CDMA a signal which is spread by multiplying aspreading code includes a chip-pattern generating unit which generates apredetermined chip pattern by performing a chip repetition for apredetermined number of repetitions to a spreading chip sequence, and amultiplying unit which multiplies to a signal including thepredetermined chip pattern which is generated by the generating unit aphase specific to the mobile station.

A mobile station in an embodiment of the invention enables a reductionin transmitting signals interfering with one another, as the frequencyspectrums of the respective mobile stations are frequency-domainorthogonal even in a case of multiple mobile stations simultaneouslyconnecting to the same base station. Such reduction of multiple-accessinterference increases the spectral usage efficiency in an isolated cellenvironment in which an effect of such interference is dominant so as toachieve an increased link capacity. As a result, when communicating byDS-CDMA, an applying of one-cell frequency reuse using only spreadingnot using chip repetition and also an applying of chip repetition in anisolated cell environment enables an implementation of an increased linkcapacity in both cell environments.

According to another aspect of the invention, a mobile station whichwirelessly transmits to a base station by DS-CDMA a signal which isspread by multiplying a spreading code includes a high-precisiontransmission timing control unit which controls transmitting timings oftransmitting signals so that a time difference at the base station amongtimings of receiving from mobile stations approaches zero.

A mobile station according to an embodiment of the invention enables anincreased link capacity without having to set at the mobile stationindividual wireless interfaces for the respective cell environments bysetting the wireless parameters of the spreading factor of the spreadingcode and the number of chip repetition to change. Furthermore, thespreading factor of the spreading code and the number of chip repetitionmay be variably controlled based on a set of controlling informationfrom a source external to the mobile stations (such as the base stationsand the networks which the mobile stations are connecting). A mobilestation is enabled an applying of one-cell frequency reuse in DS-CDMAand a setting of the optimal spreading factor and the number of chiprepetitions which take into account such effects as the reduction of MAIby chip repetition. An increase in the spectral usage efficiency so asto implement an increased link capacity is enabled. Furthermore, aswitching of cell-specific or user-specific scrambling codes, and mobilestation-specific phase sequences based on the set of information fromthe external source is enabled. The spectral usage efficiency is enabledso as to implement an increased capacity.

According to another aspect of the invention, a base station which isenabled to communicate with a mobile station includes acontrolling-information transmitting unit which transmits to the mobilestation as a set of controlling information, an information setindicating an environment of a cell which is resided by the mobilestation, or an information set indicating the power of interference fromsurrounding cells, or an information set indicating a propagationchannel condition, and a receiving unit which receives a signal which istransmitted from the mobile station, based on the set of controllinginformation, via a variably-controlling process of a spreading factorand the number of chip repetitions.

A base station in an embodiment of the invention enables a receiving ofcontrolling information from the base station or the network connectingto the base station so as to variably control the spreading factor andthe number of chip repetitions based on the controlling information.Furthermore, the base station is enabled a receiving of the transmittingsignals from the mobile stations which have undergone thevariably-controlling process.

According to another aspect of the invention, a program for wirelesstransmission, implements in a mobile station which wirelessly transmitsto a base station by DS-CDMA a spreading signal multiplied by aspreading code, a chip-pattern generating function of generating apredetermined chip pattern by performing a chip repetition for apredetermined number of repetitions to a spreading chip sequence, and amultiplying function of multiplying to a signal including thepredetermined chip pattern which is generated by the chip-patterngenerating function a phase specific to the mobile station.

A program for wireless transmission in an embodiment of the inventionenables a reduction in transmitting signals interfering with one anotheras the frequency spectrums of the respective mobile stations arefrequency-domain orthogonal even in a case of multiple mobile stationssimultaneously connecting to the same base station. Such reduction ofmultiple-access interference increases the spectral usage efficiency inan isolated cell environment in which an effect of such interference isdominant so as to achieve an increased link capacity. As a result, whencommunicating by DS-CDMA, an applying of one-cell frequency reuse usingonly spreading not using chip repetitions and also an applying of chiprepetitions in an isolated cell environment enables an implementation ofan increased link capacity in both cell environments.

According to another aspect of the invention, a method of wirelesstransmission, wherein a mobile station which wirelessly transmits to abase station by DS-CDMA a signal which is spread by multiplying aspreading code, includes a chip-pattern generating step of generating apredetermined chip pattern by performing a chip repetition for apredetermined number of repetitions to a spreading chip sequence, and amultiplying step of multiplying to a signal including the predeterminedchip pattern which is generated by the generating step a phase specificto the mobile station.

A method of wireless transmission in an embodiment of the inventionenables a reduction in transmitting signals interfering with one anotheras the frequency spectrums of the respective mobile stations arefrequency-domain orthogonal even in a case of multiple mobile stationssimultaneously connecting to the same base station. Such reduction ofmultiple-access interference increases the spectral usage efficiency inan isolated cell environment in which an effect of such interference isdominant so as to achieve an increased link capacity. As a result, whencommunicating by DS-CDMA, an applying of one-cell frequency reuse usingonly spreading not using chip repetitions and also an applying of chiprepetitions in an isolated cell environment enables an implementation ofan increased link capacity in both cell environments.

Other objects and further features of the present invention will becomeapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an overall configuration of a mobiletransmission system and a configuration of a mobile station according toa first embodiment;

FIG. 2 is a schematic diagram of major operations of a mobile stationaccording to a first embodiment;

FIG. 3 is a schematic diagram of one example of the frequency spectrumof a signal transmitted by a mobile station according to a firstembodiment;

FIG. 4 is a schematic diagram of an overall configuration of a wirelesstransmission system and a configuration of a mobile station according toa second embodiment;

FIG. 5 is a schematic diagram of an operation of a wireless transmissionsystem according to a second embodiment;

FIG. 6 is a schematic diagram of an overall configuration of a wirelesstransmission system and a configuration of a mobile station according toa third embodiment;

FIG. 7 is a sequence diagram of an operation of a wireless transmissionsystem according to a third embodiment;

FIG. 8 is a schematic diagram of major operations of a mobile stationaccording to a third embodiment;

FIG. 9 is a schematic diagram of an overall configuration of a wirelesstransmission system and a configuration of a mobile station according toa fourth embodiment;

FIG. 10 is a sequence diagram of an operation of a wireless transmissionsystem according to a fourth embodiment;

FIG. 11 is a schematic diagram of a configuration of a base stationaccording to a second, a third, and a fourth embodiment;

FIG. 12 is a schematic diagram of a variation of a configuration of abase station according to a second, a third, and a fourth embodiment;

FIG. 13 is a schematic diagram of another form of a configuration of abase station according to a second, a third, and a fourth embodiment;

FIG. 14 is a schematic diagram of an exemplary configuration of a mobilestation according to a fifth embodiment with the data rate doubled;

FIG. 15A and FIG. 15B are schematic diagrams of an exemplary frequencyspectrum of a transmitting signal with the data rate doubled;

FIG. 16 is a schematic diagram of an exemplary configuration of a mobilestation according to a fifth embodiment with the data rate halved;

FIG. 17A and FIG. 17B are schematic diagrams of an exemplary frequencyspectrum of a transmitting signal with the data rate halved;

FIG. 18 is a schematic diagram of another exemplary configuration of amobile station according to a fifth embodiment with the data ratehalved;

FIG. 19 is a schematic diagram of a configuration of a wirelesstransmission program according to the present invention;

FIG. 20 is a schematic diagram of a configuration of a mobile stationaccording to a sixth embodiment;

FIG. 21 is a schematic diagram of a configuration of a base stationaccording to a sixth embodiment;

FIG. 22 is a schematic diagram of an exemplary mobile station accordingto a fifth embodiment which changes scrambling code according toexternal controlling information;

FIG. 23 is a diagram which describes an operation of a mobile stationaccording to a sixth embodiment which applies chip repetition aftermultiplexing multiple channels;

FIG. 24 is a schematic diagram of an exemplary configuration of a mobilestation according to a fifth embodiment which changes a mobilestation-specific phase sequence according to a set of controllinginformation from an outside source;

FIG. 25 is a diagram which describes the concept of a loose transmissiontiming control which is performed in a transmission system according toa sixth embodiment;

FIG. 26 is a diagram which describes an operation of a mobile stationaccording to a sixth embodiment which inserts a guard interval per apredetermined repetition pattern;

FIG. 27 is a diagram which describes an operation of a mobile stationaccording to a sixth embodiment which sufficiently lengthens apredetermined reuse pattern;

FIG. 28 is a sequence diagram of an operation of a loose transmissiontiming control performed in a wireless transmission system according toa sixth embodiment;

FIG. 29 is a schematic diagram of a first exemplary configuration of amobile station according to a sixth embodiment which applies chiprepetition and time-multiplexes pilot channels;

FIG. 30 is a schematic diagram of a second exemplary configuration of amobile station according to a sixth embodiment which applies chiprepetition and time-multiplexes pilot channels;

FIG. 31 is a schematic diagram of a third exemplary configuration of amobile station according to a sixth embodiment which applies chiprepetition and time-multiplexes pilot channels;

FIG. 32 is a schematic diagram of an exemplary configuration of a basestation according to a sixth embodiment which measures received timingby pilot channels which apply chip repetition;

FIG. 33 is a diagram which describes a transmission timing control inaccordance with received timings of first paths of the mobile stations;

FIG. 34 is a schematic diagram of an operation of a wirelesstransmission system according to a sixth embodiment which performstransmission timing control using a common pilot signal;

FIG. 35 is a schematic diagram of a configuration of a mobile stationaccording to a seventh embodiment;

FIG. 36 is a schematic diagram of a configuration of a base stationaccording to a seventh embodiment;

FIG. 37 is a diagram which describes the concept of a stricttransmission timing control performed in a wireless transmission systemaccording to a seventh embodiment;

FIG. 38 is a schematic diagram of an exemplary configuration of a mobilestation according to a seventh embodiment which changes scrambling codebased on a set of controlling information from an outside source;

FIG. 39 is a schematic diagram of an overall configuration of a wirelesstransmission system and a configuration of a mobile station according toan eighth embodiment;

FIG. 40 is a flowchart which illustrates an operational procedure of amobile station according to an eighth embodiment;

FIG. 41 is a schematic diagram of an overall configuration of a wirelesstransmission system and a configuration of a mobile station according toa ninth embodiment;

FIG. 42 is a flowchart which illustrates an operational procedure of amobile station according to a ninth embodiment;

FIG. 43A and FIG. 43B are schematic diagrams of a time chart for a caseof applying a transmission timing control in an uplink and a case of notapplying the controlling according to the related art;

FIG. 44 is a schematic diagram of an exemplary configuration of arelated-art multi-path interference canceller;

FIG. 45 is a schematic diagram of an exemplary configuration of arelated-art chip equalizer; and

FIG. 46 is a schematic diagram of an exemplary configuration of afrequency-domain equalizer according to the related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention are describedwith reference to the accompanying drawings.

A First Embodiment

First, a configuration of a wireless transmission system according to afirst embodiment is described. As illustrated in FIG. 1, a wirelesstransmission system 1 includes a mobile station 10 and a base station100. The mobile station 10 transmits a wireless signal spread bymultiplying spreading code. The mobile station 10 includes a channelencoder 11, a data modulator 12, a spreading-code multiplier 13, a chiprepetition unit 14, a phase multiplier 15, a bandwidth limiter 16, and acarrier-frequency multiplier 17.

The channel encoder 11 performs channel coding by applyingerror-correction code such as Turbo code and convolution code. The datamodulator 12 modulates the channel-coded data. The spreading-codemultiplier 13 multiplies spreading code to the modulated data so as togenerate spreading-chip sequence. The chip-repetition unit 14 performschip repetition for a predetermined number of repetitions to thespreading-chip sequence so as to generate a predetermined chip pattern.The phase multiplier 15 multiplies to the chip pattern a phase specificto the mobile station 10. The bandwidth limiter 16 providesbandwidth-limiting to the phase-multiplied chip pattern and thecarrier-frequency multiplier 17 multiplies a carrier frequency to thechip pattern for transmission.

Then, operations of the mobile station 10 according to the presentinvention are described. First, as illustrated in FIG. 2, at thespreading-code multiplier 13, the modulated chip sequence as atransmitting signal (d1, d2, . . . ) is multiplied by spreading codehaving a spreading factor SF of 2 so as to generate a spreading chipsequence, “c1,1 ”, “c1,2 ”, “C2,1 ”, “C2,2 ”, . . . (S11). Subsequently,the chip-repetition unit 14 applies chip repetition having the number ofrepetitions CRF=4 to the spreading chip sequence. Then, thechip-repetition unit 14 sorts the chip-repeated chip sequence so as tohave the same sequential order as the spread sequence (S13). Herein, CRFstands for Chip Repetition Factor.

Chip-repeated chip sequences comprise on the frequency axis frequencyspectrums such as those illustrated in FIG. 3. As the chip sequence asdescribed above is a signal comprising a predetermined chip pattern, thefrequency spectrum becomes a comb tooth-shaped spectrum. The position ofthe comb tooth-shaped spectrum shifts as a phase specific to the mobilestation 10 is added at the phase multiplier 15 to the signal comprisinga predetermined chip pattern. Therefore, as illustrated in FIG. 3, thefrequency spectrum of the mobile station 10 and the frequency spectrumof another mobile station 200 (refer to FIG. 1) do not overlap with eachother.

Therefore, even in a case of multiple mobile stations 10 and 200simultaneously connecting to the same base station 100, the frequencyspectrum of one mobile station is orthogonal on the frequency axis tothe frequency spectrum of the other mobile station so as to reduceinterference caused by the respective transmitting signals. Herein, whenthe received timings at the base station 100 of the transmitting signalsfrom the respective mobile stations 10 and 200 are the same, thefrequency spectrum of one mobile station is orthogonal on the frequencyaxis to that of the other mobile station. This aspect is detailed in thefifth through the ninth embodiments.

Thus, in the wireless transmission system 1 according to the presentinvention, the mobile station 10, using the chip repetition and thephase multiplying, enables a generating of a transmitting signal havingthe frequency spectrum orthogonal to that of the other mobile station(such as the mobile station 200). Therefore, in an uplink in whichmultiple mobile stations are simultaneously connected to the basestation 100, a reduced transmitting signal interference and an increasedlink capacity are enabled.

A Second Embodiment

While an exemplary aspect of applying on a fixed basis SF=2 as thespreading factor and CRF=4 as the number of repetitions is illustratedin the first embodiment, in a wireless transmission system according tothe present embodiment, a mobile station comprises a function ofvariably controlling spreading factor of spreading code and the numberof chip repetitions.

A wireless transmission system 2 according to the second embodiment hasthe same basic configuration as the wireless transmission system 1 asdetailed in the first embodiment. Therefore, numerals of the same column(with the same tail-ends) are assigned to the mobile station and itselements so as to omit the description while detailing below thedifferences from the first embodiment, referring to FIG. 4 and FIG. 5.

FIG. 4 is a schematic diagram of an overall configuration of thewireless transmission system 2 and a configuration of a mobile station20 according to the present embodiment. The controller 28, which is anelement specific to the mobile station 20, variably controls thespreading factor of the spreading code and the number of chiprepetitions based on the controlling information sent from the basestation as an external apparatus. This controlling information includesthe spreading factor and the number of chip repetitions to be applied tothe mobile station 20.

Below, referring to a sequence diagram in FIG. 5, an operation of thewireless transmission system 2 is described.

In S21, the spreading factor and the number of chip repetitions to beused by the mobile station 20 is reported from the base station 100 tothe mobile station 20. Such reporting may be by controlling informationsent as broadcast information to an indefinite number of mobilestations, or may be by controlling information sent to a specific mobilestation 20.

In S22, at the mobile station 20, a transmitting signal is generatedbased on the spreading factor and the number of chip repetitionsreported in S21. The generating of the transmitting signal is performedaccording to the same procedure as the generating of the transmittingsignal in the first embodiment (S11 through S13 as illustrated in FIG.2). The generated signal is sent from the mobile station 20 to the basestation 100 via a wireless channel (S23). Then, the signal received fromthe base station 100 is demodulated according to the spreading factorand the number of chip repetitions reported from the base station 100 inS21 (S24).

As described above, using the wireless transmission system 2 accordingto the present embodiment, the mobile station 20 generates atransmitting signal based on the spreading factor of the spreading codeand the number of chip repetitions. In other words, the base station 100enables an appropriate changing of the spreading factor and the numberof chip repetitions to be used in the signal generating at the mobilestation 20. Therefore, a generating of a transmitting signal using thewireless parameters suitable for the respective cell environmentswithout providing at the mobile station 20 individual wirelessinterfaces for the respective cell environments is enabled.

Furthermore, this transmitting signal comprises the frequency spectrumorthogonal on the frequency axis to the frequency spectrum of thetransmitting signal from the other mobile station 200. Therefore, areduction of interference in a transmitting signal in an uplink wheremultiple mobile stations 20 and 200 simultaneously connect to the basestation 100 so as to increase the link capacity in an isolated cellenvironment is enabled.

A Third Embodiment

While an exemplary aspect which variably controls the spreading factorand the number of chip repetitions based on the spreading factor and thenumber of chip repetitions reported from the base station is shown inthe second embodiment, the mobile station comprises a function ofvariably controlling the spreading factor and the number of chiprepetitions based on the cell environment reported from the base stationin the wireless transmission system according to the present embodiment.

A wireless transmission system 3 according to the third embodiment hasthe same basic configuration as the wireless transmission system 2detailed in the second embodiment. Therefore, numerals of the samecolumn (with the same tail-ends) are assigned to the mobile station andits elements so as to omit the description as well as detailing belowthe differences from the second embodiment, referring to FIG. 6 throughFIG. 8.

FIG. 6 is a diagram of an overall configuration of the wirelesstransmission system 3 according to the present embodiment and aconfiguration of a mobile station 30. The controller 38, which is anelement specific to the mobile station 30, variably controls thespreading factor of the spreading code and the number of chiprepetitions based on the controlling information indicating the cellenvironment transmitted from the base station 100 as an externalapparatus. More specifically, the controller 38 performs a controllingoperation which sets the number of chip repetitions by thechip-repetition unit 34 to “1” in a case that the cell environment whichthe mobile station 200 falls within is a multi-cell environment. Inother words, it is set such that the chip repetition is not performed sothat only the spreading factor is set. Hereby, the one-cell frequencyreuse is achieved so as to increase the link capacity.

On the other hand, in a case where the cell environment which the mobilestation 30 falls within is an isolated cell environment, the controller38 performs controlling which increases the number of chip repetitionswhile decreasing the spreading factor. Preferably, the number of chiprepetitions is set to be equal to 1 or more, for example CRF of around4, so as to decrease the magnitude of the spreading factor only for thenumber of chip repetitions. Hereby, as in the wireless transmissionsystem according to the first and the second embodiments, the frequencyspectrum of the mobile station 30, and that of the mobile station 300where the mobile stations simultaneously connect to the base station100, are orthogonal to each other so as to reduce interference betweenthe transmitting signals from the respective mobile stations. Suchcontrolling is more effective in an isolated cell environment in whichthe reduction in the spectral usage efficiency due to multiple accessinterference is especially large.

Below, an operation of the wireless transmission system 3, referring toFIG. 7, is described. In S31, the cell environment which the mobilestation 30 falls within (one of a multi-cell environment and an isolatedcell environment) is reported to the mobile station 30 from the basestation 100. Such reporting may be by controlling information sent to anindefinite number of mobile stations (broadcast information), or may beby controlling information sent to a specific mobile station 20.

In S32, a transmitting signal is generated at the mobile station 30based on the spreading factor and the number of chip repetitions whichcorrespond to the cell environment reported in S31. The generating ofthe transmitting signal is performed according to the same procedure asthe generating of the transmitting signal according to the firstembodiment (S11 through S13 as illustrated in FIG. 2). The generatedsignal is transmitted via a wireless channel from the mobile station 30to the base station 100 (S33). Then, the signal from the base station100 is demodulated based on the spreading factor and the number of chiprepetitions which correspond to the cell environment reported from thebase station 100 in S31 (S34).

Below, a flow of major processes executed at the mobile station 30 isdescribed, referring to FIG. 8. The wireless parameters set up at thespreading-code multiplier 33, the chip-repetition unit 34 and the phasemultiplier 35, based on the controlling information input at thecontroller 38, are appropriately changed.

In other words, in a case where the controlling information reports amulti-cell environment, P11 and P21 in FIG. 8 are applied as thewireless parameters. As a result, the spreading code (SF cellular)generated at the spreading code generator 33-1 is multiplied by thespreading-code multiplier 33 and then the scrambling code generated atthe scrambling code generator 39-1 is multiplied by the scrambling-codemultiplier 39 (not illustrated in FIG. 6). Subsequently, the outputtingis performed without performing chip repetition at the chip-repetitionunit 34 (CRF=1).

On the other hand, in a case where the controlling information indicatesan isolated cell environment, P12 and P22 (hatched in FIG. 8) areapplied as the wireless parameters. As a result, the spreading codegenerated at the spreading-code generator 33-1 by the spreading-codemultiplier 33 (SF hot spot) is multiplied and then the scrambling codegenerated at the scrambling-code generator 39-1 is multiplied. Then, thechip repetition where CRF>1 at the chip-repetition unit 34 is performedso as to generate a signal having a predetermined chip pattern and tomultiply an user-specific phase. Hereby, the chip pattern is keptconstant.

As described above, using the wireless transmission system 3 accordingto the third embodiment, the mobile station 30 uses the wirelessparameters to variably control the spreading factor of the spreadingcode and the number of chip repetitions based on the cell environment.Hereby, an increased link capacity using a single wireless interfaceregardless of the cell environment which the mobile station 30 fallswithin is enabled.

A Fourth Embodiment

While in the third embodiment an exemplary aspect which variablycontrols the spreading factor of the spreading code and the number ofchip repetitions based on the cell environment which the mobile stationfalls within is described, the mobile station in a wireless transmissionsystem 4 according to the present embodiment comprises a function ofvariably controlling the spreading factor and the number of chiprepetitions according to the number of mobile stations simultaneouslyconnected to a base station. The wireless transmission system 4according to the fourth embodiment comprises the same basicconfiguration as the wireless transmission systems 2 and 3 detailed inthe second and third embodiments. Therefore, numerals of the same column(with the same tail-ends) are assigned to the mobile station and itselements so as to omit the description while detailing below thedifferences from the second and the third embodiments, referring to FIG.9 and FIG. 10.

FIG. 9 is a diagram of an overall configuration of the wirelesstransmission system 4 and the configuration of a mobile station 40 in acase of wireless connections from the three mobile stations 40, 200, and210 to the base station 100. The controller 48, which is an elementspecific to the mobile station 40, variably controls the spreadingfactor of the spreading code and the number of chip repetitions based onthe controlling information indicating the number of simultaneousconnections transmitted from the base station 100 as an externalapparatus.

More specifically, the controller 48 performs the controlling todecrease the spreading factor of the spreading code with an increase inthe number of mobile stations connected to the base station 100 as wellas to increase the number of chip repetitions. Interference among thetransmitting signals from the respective mobile stations increases asthe number of mobile stations simultaneously connected increases. Thus,the arrangement such that the transmitting signals from the respectivemobile stations 40, 200, and 210 being connected to the base station 100are orthogonal on the frequency axis to one another with an increasednumber of chip repetitions enables a reduction of multiple-accessinterference so as to increase the spectral usage efficiency and thelink capacity. As a result, an increase in the link capacity whilesuppressing interference among the respective mobile stations isenabled.

Below, an operation of the wireless transmission system 4 is describedby referring to FIG. 10.

In S41, the number of simultaneously-connecting mobile stations that isthe number of mobile stations currently connected to the mobile station40 is reported from the base station 100 to the mobile station 40. Suchreporting may be by controlling information sent from the base station100 as broadcast information to an indefinite number of mobile stations,or may be by controlling information sent to a specific mobile station40.

In S42, a transmitting signal is generated at the mobile station 40based on the spreading factor and the number of chip repetitions whichcorrespond to the number of simultaneously-connected mobile stationsreported in S41. The generating of the transmitting signal is performedaccording to the same procedure as the generating of the transmittingsignal according to the first embodiment (S11 through S13 as illustratedin FIG. 2). The generated signal is transmitted via a wireless channelfrom the mobile station 40 to the base station 100 (S43). Then, thesignal received from the base station 100 is demodulated in S41 based onthe spreading factor and the number of chip repetitions which correspondto the number of simultaneously-connecting mobile stations reported fromthe base station 100 (S44).

As described above, according to the wireless transmission system 4according to the fourth embodiment, the mobile station 40 variablycontrols the spreading factor of the spreading code and the number ofchip repetitions based on the number of mobile stations simultaneouslyconnected to the base station which the mobile station 40 is connectedto. Hereby, the mobile station 40 is enabled an increased link capacityby using a single wireless interface regardless of the resident cellenvironment.

Next, a configuration of the base station 100 according to the second,the third, and the fourth embodiments is described, referring to FIG.11. The base station 100 receives a signal transmitted from the mobilestations 20, 30, and 40. As illustrated in FIG. 11, the base station 100comprises a carrier-frequency multiplier 101, a bandwidth limiter 102, aphase multiplier 103, a chip-repetition combiner 104, a despreading unit105, a data demodulator 106, and a channel decoder 107.

The base station 100 reconstructs a binary data sequence from thereceived signal according to an opposite process of generating thetransmitting signal at the mobile station. In other words, thecarrier-frequency multiplier 101 multiplies a carrier frequency to thereceived signal so as to convert the received signal into a digitalbaseband signal. The bandwidth limiter 102 provides a bandwidth limitingto the digital baseband signal. The phase multiplier 103 restores thephase of the signal multiplied at the transmitting mobile station to theoriginal phase. As a result, a signal having a predetermined chippattern is generated.

The chip repetition combiner 104 uses the number of chip repetitions,which is the same as the number of chip repetitions reported to thetransmitting mobile station, to recombine from the signal as describedabove a chip-repeated signal. As a result, a spreading chip sequence isgenerated. The despreading unit 105 multiplies to the chip sequence thespreading code having the same spreading factor as the spreading factorreported to the transmitting mobile station so as to restore thereceived signal to the modulated data before spreading. The datademodulator 106 demodulates the modulated data while the channel decoder107 decodes an error-correction code so as to channel-decode data afterdemodulation. As a result of the channel decoding process, the binarydata sequence input to the mobile station is reconstructed.

The controller 108, based on the controlling information transmitted tothe mobile stations 20, 30, and 40, variably controls the spreadingfactor of the spreading code to be used at the despreading unit 105 andthe number of chip repetitions to be used at the chip-repetitioncombiner 104.

Moreover, the base station 100 as illustrated in FIG. 12, based on thecontrolling information sent from one of the mobile stations 20, 30, and40, may determine the number of chip repetitions and the spreadingfactor to be used in the reconstruction process of the received signalat the controller 108.

Furthermore, as illustrated in FIG. 13, the base station 100 maydetermine, based on both the controlling information transmitted to oneof the mobile stations from the base station 13 and the controllinginformation transmitted from the mobile station, the number of chiprepetitions and the spreading factor to be used in the reconstructionprocess of the received signal. Hereby, the base station 100 is enableda collating of the controlling information transmitted to the mobilestation with the controlling information received from the mobilestation so that a simple and speedy confirmation as to whether thevariable controlling of the spreading factor and the number of chiprepetitions is performed. In such an aspect, a more accurate signaltransmitting and receiving is enabled, assuming that the receiving ofthe signal from the mobile station is performed in a case that avariable controlling is appropriately performed.

A Fifth Embodiment

Incidentally, while in the first through the fourth embodiments the datarate of the transmitting signal from the mobile station is assumed to beconstant, it is also possible to change the comb tooth-shaped setsorthogonal to one another in accordance with data rates desired by therespective mobile stations.

Below, as an example, are embodiments for a case of doubling the datarate desired by the respective mobile stations and for a case of halvingsuch data rate are described.

First, the embodiment in which the data rate desired by the respectivemobile stations is doubled is described using FIG. 14, FIG. 15A and FIG.15B.

FIG. 14 is a schematic diagram of a configuration of a mobile stationaccording to the present embodiment. Needless to say, as theconfiguration is n parallel, the data rate would be multiplied by n.

In FIG. 14, the mobile station comprises a serial-to-parallel converter201, spreading-code generators (C-1 through C-n) 202-1 through 202-n,multipliers 203-1 through 203-6, scrambling-code generators (SC-1through SC-n) 204-1 through 204-n, chip-repetition units 205-1 through205-n, mobile station-specific phase sequence (P-1 through P-n)generators 206-1 through 206-n, and a combiner 207.

The serial-to-parallel converter 201 serial-to-parallel converts aninput symbol sequence so as to convert to n sequences. The respectiveparallel symbol sequences output from serial-to-parallel converter 201are multiplied with the spreading codes (C-1 through C-n) generated atthe spreading-code generators 202-1 through 202-n and then with thescrambling codes (SC-1 through SC-n) generated at the scrambling codegenerators 204-1 through 204-n. Thereafter, the chip repetition isperformed at the chip-repetition units 205-1 through 205-n. Herein, thespreading codes and the scrambling codes multiplied to the respectivesequences may be common codes or different codes.

The respective parallel symbol sequences after chip repetition arephase-multiplied with the phase sequences (P-1 through P-n) generated atthe mobile station-specific phase sequences generators 206-1 through206-n so as to be combined for outputting at the combiner 207. Herein,the phase sequence used in the phase multiplying is shifted to anothercomb-tooth set so that a multiplying of a different phase sequence everyn sequences is needed.

Such chip-repeated sequence combined at the combiner 207 comprises afrequency spectrum on the frequency axis as illustrated in FIG. 15A andFIG. 15B.

FIG. 15A and FIG. 15B are schematic diagrams of an exemplary frequencyspectrum of a transmitting signal in which the data rate desired by themobile station is doubled.

As illustrated in FIG. 15B, in a case of doubling the data rate desiredby the mobile station (to the data rate B) according to the presentembodiment, the hatched comb-toothed spectrum set as well as the shadedcomb-toothed spectrum set are assigned to one mobile station so as totransmit different data symbols for the respective sets. Hereby, atransmitting of a transmitting signal from a mobile station at the datarate double the data rate A as indicated in FIG. 15A is enabled.

Next, an example of a case in which the data rates desired at therespective mobile stations is halved is described using FIG. 16, FIG.17A, and FIG. 17B.

The mobile station according to the present embodiment has basically thesame configuration as the configuration of the mobile station asillustrated in FIG. 14. Therefore, numerals of the same column (with thesame tail-ends) are assigned to its elements so as to omit thedescription in addition to describing below the differences from theembodiment as described above, referring to FIG. 16, FIG. 17A, and FIG.17B.

The difference between the mobile station as illustrated in FIG. 16 andthe mobile station as illustrated in FIG. 14 is that the input symbolsequence is not serial-to-parallel converted, but ratherparallel-copied. In other words, according to the present embodiment,the duplicator 211 is used in lieu of the serial-to-parallel converter201 so as to duplicate the input symbol sequence to n sequences.Hereafter the same process as the mobile station as illustrated in FIG.16 is performed.

FIG. 17A and FIG. 17B are schematic diagrams of an example of thefrequency spectrum of a transmitting signal with the data rate desiredby the mobile station halved.

As illustrated in FIG. 17B, in a case of halving the data rate desiredby the mobile station according to the present embodiment, the hatchedcomb-toothed spectrum set as well as the shaded comb-toothed spectrumset are allocated to one mobile station so as to transmit the same datasymbols at the respective sets. Hereby, a transmission of a transmittingsignal of the mobile station at a halved data rate relative to the datarate A as illustrated in FIG. 17A is enabled. A transmitting having suchredundancy enables characteristic improvement due to afrequency-diversity effect.

Furthermore, as another example of a configuration of a mobile stationwhich halves the data rate desired by the mobile station (to the datarate C), a configuration as illustrated in FIG. 18 may also be possible.The mobile station as illustrated in FIG. 18 is comprised by combiningthe frequency-domain spreading with the time-domain spreading(two-dimensional spreading). The configuration of the mobile stationaccording to the present embodiment is basically the same as theconfiguration of the mobile station as illustrated in FIG. 16.Therefore, herein, the difference from the mobile station as illustratedin FIG. 16 is described. The mobile station as illustrated in FIG. 18multiplies at the multiplier 203-7 the spreading code Cfreq generated atthe Cfreq 212 before the serial-to-parallel conversion to the symbolsequence so as to serial-to-parallel convert the spreading signal.Subsequently the same process as in the mobile station as illustrated inFIG. 16 is performed.

As described above, according to the mobile station according to thefifth embodiment, a change of the orthogonal comb tooth-shaped setsallocated to a mobile station according to the data rate desired by therespective mobile stations and a flexible assignment of the data rate inaccordance with a change in the communications environment of the mobilestation while obtaining the MAI reduction effect is enabled.

Moreover, while the exemplary cases of doubling and halving the datarate desired by the mobile station according to the fifth embodiment aredescribed, other multiplying factors may also be applicable.Furthermore, the chip pattern and the phase sequence, or the frequencyband (whether neighboring or distant) may be changed in accordance withthe communications condition of the respective mobile stations. An useof proximate frequency bands by neighboring mobile stations enables areduction of inter-channel interference which impacts the surroundings.In addition, further enhancement of the frequency-diversity effect isenabled.

Next, a program for performing the process of generating a transmittingsignal from a binary data sequence is described. As illustrated in FIG.19, a wireless transmission processing program 310 is stored at aprogram storage area 300 a comprised in a recording medium 300. Awireless transmission processing program 310 comprises a main module 311which superintends the process of generating a transmitting signal, achannel-coding module 312, a data modulation module 313, aspreading-code multiplying module 314, a chip-repetition module 315, aphase-multiplying module 316, a bandwidth-limiting module 317, acarrier-frequency multiplying module 318, and a controlling module 319as its elements.

The functions implemented by executing the channel-coding module 312 arethe same as the functions of the channel-encoders 11, 21, 31, and 41 ofthe mobile stations 10, 20, 30, and 40. In other words, the channelcoding module 312 applies the error-correction codes such as the Turboand the convolution codes to the input binary data sequence so as toenable an execution of the channel-coding process at the mobile station.The functions implemented by executing the data modulation module 313are the same as the functions of the data modulators 12, 22, 32, and 42.In other words, the data modulation module 313 enables at the mobilestation an execution of the process of modulating channel-coded data.

The functions implemented by executing the spreading-code multiplyingmodule 314 are the same as the functions of the spreading-codemultiplying at the mobile station as described above. In other words,the spreading-code multiplying module 314 multiplies the spreading codeto modulated data so as to enable an execution at the mobile station ofthe process of generating a spreading chip sequence. The functionsimplemented by executing the chip repetition module 315 are the same asthe functions of the chip-repetition units 14, 24, 34, and 44. In otherwords, the chip repetition module 315 performs chip repetition to thespreading chip sequence for a predetermined number of repetitions so asto enable the mobile station to execute the process of generating apredetermined chip pattern.

The functions implemented by executing the phase-multiplying module 316are the same as the functions of the phase multipliers 15, 25, 35, and45 of the mobile station as described above. In other words, the phasemultiplying module 316 enables the mobile station an execution of theprocess of multiplying the mobile station-specific phase to the chippattern. The functions implemented by executing the bandwidth-limitingmodule are the same as the functions of the bandwidth limiters 16, 26,36, and 46 of the mobile station as described above. In other words, thebandwidth-limiting module 317 enables the mobile station an execution ofthe process of providing a bandwidth limiting to the phase-multipliedchip pattern.

The functions implemented by executing the carrier-frequency multiplyingmodule 318 are the same as the functions of the carrier-frequencymultipliers 17, 27, 37, and 47 of the mobile station as described above.In other words, the carrier-frequency multiplying module 318 enables themobile station an executing of the process of multiplying the carrierfrequency to the chip pattern for transmission. The functionsimplemented by executing the controlling module 319 are the same as thefunctions of the controllers 28, 38, and 48 of the mobile station asdescribed above. In other words, the controlling module 319 enables themobile station an executing of the process of variably controlling thespreading factor of the spreading code and the number of chiprepetitions.

Moreover, the wireless transmission processing program 310 may beconfigured in a manner such that all or a portion of that program istransmitted via a transmission medium such as a communications line soas to be received by an information and communications equipment, suchas a mobile terminal, for recording (including installation).

While the embodiment as described above is for a case of applying onlychip repetition at the mobile station, hereafter the embodiment for acase of a combined use of chip repetition and transmission timingcontrol is described.

A Sixth Embodiment

A configuration of a wireless transmission system according to a sixthembodiment is described. The wireless transmission system according tothe sixth embodiment as in previously described embodiments, comprises amobile station and a base station, the mobile station having thefunctions of chip repetition and transmission timing control. On theother hand, the receiver of the base station comprises the functions ofa multi-path interference canceller, a chip equalizer, and afrequency-domain equalizer. A summary of the functions of the mobilestation and the base station according to the sixth embodiment isprovided below.

TYPE OF INTERFERENCE INTERFERENCE INTERFERENCE SIGNAL FROM OTHER BYMULTI-PATH MOBILE STATIONS PROPAGATION OF (MULTIPLE-ACCESS TRANSMITTINGSIGNAL INTERFERENCE) (MULTI-PATH INTERFERENCE) APPLIED COMBINED USE OFREMOVAL OF MULTI-PATH TECH- CHIP REPEATING AND INTERFERENCE NOLOGIESTRANSMISSION AT THE BASE STATION TIMING CONTROL (MULTI-PATH INTERFERENCECANCELLER, CHIP EQUALIZER, FREQUENCY- DOMAIN EQUALIZER)

Next, a configuration of a mobile station according to the sixthembodiment is described. FIG. 20 is a schematic diagram of aconfiguration of a mobile station. A description of an operation of chiprepetition applied to the mobile station which has already been providedis omitted.

In FIG. 20, the mobile station comprises as a transmitter atransmitting-data generator 221, a pilot-channel generator 222, an adder223, a spreading-code multiplier 224, a scrambling-code multiplier 225,a chip-repetition unit 226, and a transmitting-timing controller 227,and as a receiver a receiving-data demodulator/decoder 228, and atransmission-timing control information detector 229.

Below an operation of the mobile station is described.

(An Operation of a Transmitter)

The pilot channel generated at the pilot-channel generator 222 and thetransmitting data generated at the transmitting data generator 221 areadded at the adder 223 so as to be multiplexed, and then spreading-codemultiplying at the spreading-code multiplier 224 and scrambling-codemultiplying at the scrambling-code multiplier 225 are performed. Then,chip repetition is performed at the chip-repetition unit 226 so as togenerate the comb tooth-shaped frequency spectrum as a transmittingsignal. Such generated transmitting signal is transmitted at atransmitting timing controlled at the transmission timing control unit227. The transmission timing control unit 227 controls the transmittingtimings of the transmitting signals based on the reporting from thetransmission-timing control information detector 229 to be describedbelow.

(An Operation of a Receiver)

The signal received at the mobile station (the received signal) is inputto the received data demodulator/decoder 228 so as to be output asdecoded sequence data after being data-demodulated and data-decoded in acase of the received signal being a data signal. On the other hand, in acase that the received signal is a controlling signal which includes thetransmitting timing information, the received signal is sent to thetransmission timing control information detector 229 via the receiveddata demodulator/decoder 228. The transmission timing controlinformation detector 229 detects a transmitting timing information fromthe received signal so as to report to the transmitting timingcontroller 228 of the transmitter.

Next, a configuration of a base station according to the sixthembodiment is described. FIG. 21 is a schematic diagram of aconfiguration of a base station. A description of an operation of amulti-path interference canceller, a chip equalizer, and afrequency-domain equalizer already described herein is omitted.

In FIG. 21, this base station comprises a transmission-timing controlinformation generator 111, a transmitting-signal generator 112, andprocessors 113-1 through 113-n of mobile stations 1 through n. As theconfigurations of the processors 113-1 through 113-n of the mobilestations a through n are the same, an exemplary configuration of theprocessor 113-1 of the mobile station a is described. The processor113-1 of the mobile station a comprises as tranmitting processingfunctions a transmitting data generator 114 and an adder 115 and asreceiving processing functions a received data demodulator/decoder 116which removes multi-path interference, a received datademodulator/decoder 116, a chip repetition reconstruction unit 117, anda received timing detector 118.

Below, an operation of the base station configured as described above isdescribed.

The signals from the respective mobile stations (mobile station athrough n) received at the base station undergo at the correspondingprocessors (the processors of the mobile stations a through n) 113-1through 113-n the processing of the received signals.

The received signals from the respective mobile stations a through ninput from the processors 113-1 through 113-n of the respective mobilestations a through n are multiplied with the mobile station-specificphase sequences comprised in the mobile stations a through n so as toundergo at the chip repetition reconstruction unit 117 an operationwhich restores chip repetition. Hereby, such demultiplexed signals fromthe respective mobile stations a through n undergo the removal ofmulti-path interference at the received data demodulator/decoder 116 sothat the transmitting data are reconstructed for outputting as thedecoded data sequence.

On the other hand, the received timing detector 118 uses the receivedpilot channels transmitted from the respective mobile stations a throughn so as to perform the detection of the received timings. Herein, thedetected received timing information is sent to the transmission timingcontrol information generator 111 where the transmission timing controlinformation such that the received timings at mobile stations a throughn coincide with one another is generated.

Such generated transmission timing control information is sent to theadder 115 so as to be added with the transmitting data generated at thetransmitting data generator 114 for transmission to the transmittingsignal generator 112. The transmitting signal generator 112 includes thetransmission timing control information as described above for reportingto the respective mobile stations.

As described above, in the wireless transmission system according to thesixth embodiment, mobile stations perform in addition to chip repetitiona controlling of the transmitting timings so that the received timingsat the base station coincide when the transmitting signals are sent tothe base station, enabling a further reduction of the effect ofmultiple-access interference as the frequency spectrum of the respectivemobile stations becomes fully orthogonal with one another on thefrequency axis.

Furthermore, at the base station, transmitting signals with a combineduse of chip repetition and the transmission timing control received fromthe mobile stations are multiplied with the phase sequencescorresponding to the respective mobile stations so as to restore therepeated chip pattern to the original form to demultiplex into thesignals from the respective mobile stations. Then, those demultiplexedsignals of the respective mobile stations are applied to the multi-pathinterference canceller, the chip equalizer, and the frequency-domainequalizer as illustrated in FIG. 44 through 46 in order to removemulti-path interference caused by the multi-path propagation of the owntransmitting signal so as to reduce the effect of multiple interference.In other words, the receiver of the base station which performs theremoval of interference caused by its own multiple signal enables asimplifying of the base station receiver configuration relative to theconfiguration which removes multiple-access interference from othermobile stations.

In the wireless transmission system according to the present embodiment,the mobile station comprises a function of changing the scrambling codemultiplied to the spreading chip sequence. Below an operation of themobile station as described above is described.

In FIG. 22, the data-symbol sequence is multiplied at the multiplier242-1 with the spreading code generated at the spreading-code generator241 so as to be multiplied at the multiplier 242-2 with the scramblingcode. The scrambling code used in the multiplying of the scrambling codeis used by switching at the scrambling code switching controlling unit245 to one of the cell-specific scrambling code and the user-specificscrambling code. In the present embodiment, the scrambling codeswitching controlling unit 245 performs switching based on the externalcontrolling information which instructs the switching of the scramblingcode. As the external controlling information, the cell-configurationinformation indicating one of the multi-cell environment and theisolated cell environment, or one of the cell-specific and user-specificscrambling codes is used in accordance with the information such as thenumber of simultaneously-connecting mobile stations in an uplink.Subsequent to the scrambling code multiplying, the chip-repeatedsequence is output via chip repetition at the data reuse unit 243 andthe multiplying with the phase sequence generated at the mobilestation-specific phase sequence generator 244 (multiplied at themultiplier 242-a).

Furthermore, in the wireless transmission system according to thepresent embodiment, the mobile station multiplies spreading codesdifferent for the respective channels so as to multiplex multiplechannels and then to perform chip repetition. Below, an operation of themobile station is described, referring to FIG. 23.

In FIG. 23, a multiplying at the mobile station of different spreadingcodes having SF=2 to the different symbol sequences of channels A and B,or (a1, a2, . . . ) and (b1, b2, . . . ) enables a code-multiplexing ofthe two channels of the spreading chip sequence “a1,1”, “a1,2”, “a2,1”,“a2,2”, . . . , “b1,1”, “b1,2”, “b2,1”, “b2,2”. According to the presentembodiment, a performing of chip repetition to such code-multiplexedchip sequence of channels A and B (“x1,1”, “x1,2”, “a2,1”, “x2,2”, . . .) enables a flexible multiplexing of different channels within the combtooth-shaped spectrum. Besides, for the channel multiplexing, there maybe, for example, a case of multiplexing multiple data channels inaccordance with the data transmission rate and a case of multiplexing adata channel and a controlling channel.

Furthermore, in a wireless transmission system according to the presentembodiment, a mobile station comprises a function of changing a mobilestation-specific phase sequence based on the external controllinginformation. Below an operation of the mobile station is described. Thedescription of the process up to chip repetition according to thepresent embodiment which is the same as the process according to theembodiment as illustrated in FIG. 22 is omitted.

In FIG. 24, the external controlling information is input to the mobilestation-specific phase sequence generator 255. According to the presentembodiment, an inclusion as the external controlling information of thephase sequence information to be used as the information for reportingfrom the base station to the respective mobile stations enables adetermination of the mobile station-specific phase sequence based onthat reporting information. Furthermore, the method of determining themobile station-specific phase sequence is not limited the method asdescribed above. For example, it may comprise an aspect such that therespective mobile stations autonomously determine the mobilestation-specific phase sequence by a predetermined method.

As described above, in order that the chip-repeated signals at therespective mobile stations be orthogonal to one another in the frequencydomain, the received timings at the base station of the signals from therespective mobile stations need to coincide. Thus, in the wirelesstransmission system according to the present embodiment, the basestation comprises a function of performing a loose transmitting timingcontrol of the respective mobile stations so that the offsets among thereceived timings at the mobile stations are contained to within apredetermined time difference.

Below, the concept of a loose transmission timing control performed atthe base station is described, referring to FIG. 25. Herein, for thebrevity of the description, the target mobile stations for thetransmission timing control are limited to the two mobile stations ofthe mobile station 1 and the mobile station 2.

According to the present embodiment, the loose transmission timingcontrol is referred to a loose control of transmission timing so as tocontain the time difference T−D between the received timings of areceived symbol I-1 at the mobile station 1 and that of a receivedsymbol j-2 at the mobile station 2 to within a predetermined timedifference. This received time difference T−D needs only to be a timedifference necessary for obtaining a frequency-domain orthogonalitybetween the mobile stations and may be considered, for example, to beone or around a few blocks of a repetition pattern.

Such base station according to the present embodiment enables areduction of the controlling load by performing transmission timingcontrol of the respective mobile stations while allowing for the timedifference T−D of the received timings.

Incidentally, in a case of applying the loose transmission timingcontrol as described above, there may be a case in which multiple-accessinterference may occur as an offset of the received timings among themobile stations at the base station causes the frequency-domainorthogonality of the chip-repeated signals at the respective mobilestations to be lost. Thus, in the wireless transmission system accordingto the present embodiment, the mobile station comprises a function ofadding a guard interval so that the chip-repeated transmitting signalare fully orthogonal in the frequency domain. Below an operation of themobile station is described, referring to FIG. 26.

In FIG. 26, an exemplary case of generating a guard interval byduplicating the respective portions of the tail-end and the head of thechip pattern generated by chip repetition to the tail-end and the headof the corresponding chip pattern is illustrated.

While the base station receives from the respective mobile stations suchsignal having the guard interval as described above added, thechip-repeated signals of the respective mobile stations are receivedwith a frequency-domain orthogonality when the time difference T−D ofthe received timings due to the loose transmission timing control issmall relative to the total length T−G of the guard interval generatedas described above. In other words, even in a case of applying a loosetransmission timing control, reduction of multiple-access interferenceis enabled by inserting at the mobile station the guard interval asdescribed above.

Furthermore, the mobile station as described above comprises a functionof setting the length of the chip-repeated chip pattern longer than thetime difference at the base station of the received timings of therespective mobile stations from a point of view of reducingmultiple-access interference. Below an operation of the mobile stationis described, referring to FIG. 27.

In FIG. 27, the mobile station sets the chip-repeated chip patternlength T−S to be sufficiently longer than the time difference T−D of thereceived timings at the respective mobile stations. Hereby, reduction ofthe effect of losing frequency-domain orthogonality of the signals ofthe respective mobile stations and of multiple-access interference isenabled. Furthermore, according to the present embodiment, improvementin transmission efficiency is enabled by not performing the inserting ofthe guard interval as illustrated in FIG. 26 so as to reduce redundantdata.

Next, a specific example of the transmission timing control performed ina wireless transmission system is described, referring to the sequencediagram in FIG. 28.

In FIG. 28, in S51, the signals for measuring at the base station 100the differences among the respective mobile stations 70-1 through 70-nof the received timings are transmitted from the respective mobilestations 70-1 through 70-n. The base station 100 receives the signals asdescribed above transmitted from the respective mobile stations 70-1through 70-n so as to measure the received timings of the respectivemobile stations.

In S52, the base station 100 computes the transmitting timings of therespective mobile stations 70-1 through 70-n so that the receivedtimings of the respective mobile stations 70-1 through 70-n coincide soas to transmit the signal reporting these transmitting timings to therespective mobile stations 70-1 through 70-n. The respective mobilestations 70-1 and 70-n demodulate the signal as described above reportedfrom the base station 100.

In S53, the respective mobile stations 70-1 through 70-n transmit thesignals based on the transmitting timings obtained after demodulation asdescribed above. Hereby, the base station 100 enables reception of thesignal so that the received timings of the signals from the respectivemobile stations 70-1 through 70-n coincide.

Thus, the base station 100 according to the present embodiment generatesthe transmission timing control information for the respective mobilestations 70-1 through 70-n based on the differences among the respectivemobile stations of the received timings. In other words, a setting ofmore coarse resolution of such transmitting timing information enablesimplementation of loose transmission timing control which handles anoperation as a step-like operation. On the other hand, a setting offiner resolution of the information on the transmitting timings to bereported to the respective mobile stations enables an implementation ofmore strict transmission timing control.

As described above, the base station according to the present embodimentcomprises the function of measuring the received timings of therespective mobile stations for reporting transmission timing controlinformation to the respective mobile stations. As a signal used formeasuring this received timing, a pilot signal may be considered. Inother words, using the wireless transmission system according to thepresent embodiment, the mobile station comprises a function ofmultiplexing to the transmitting signal a pilot channel having a knownamplitude and phase so as to perform chip repetition. Below the methodof multiplexing the pilot channel at the mobile station is described,referring to FIG. 29 through FIG. 31.

(A First Multiplexing Method of Pilot Channel)

FIG. 29 is a schematic diagram of an exemplary embodiment in a case oftime-multiplexing a data channel transmitting a data chip and a pilotchannel transmitting a pilot symbol. As illustrated in FIG. 29, the datasymbol input from the data symbol sequence input port and the pilotsymbol input from the pilot symbol sequence input port are temporallyswitched at the switch 260 so as to be input at the multiplier 262-1 andthen to be multiplied at the same multiplier 262-1 the spreading codegenerated at the spreading-code generator 261. Thereafter, as describedabove, scrambled-code multiplying and chip repetition are performed soas to output as the chip-repeated sequence.

(A Second Multiplexing Method of Pilot Channel)

FIG. 30 is an exemplary embodiment in a case of assigning differentspreading codes to a data channel transmitting a data symbol and a pilotchannel transmitting a pilot symbol so as to code-multiplex. Asillustrated in FIG. 30, the data symbol input from the data symbolsequence input port and the pilot symbol input from the pilot symbolsequence input port are respectively multiplied by the differentspreading codes. More specifically, the data symbol is multiplied by thespreading code generated at the spreading-code generator for data symbol271 while the pilot symbol is multiplied by the spreading code generatedat the spreading code generator for pilot symbol 272.

Such spreading-code multiplied data symbol and pilot symbol arecode-multiplexed at the adder 274 so as to undergo scrambling-codemultiplying and chip repetition for outputting.

(A Third Multiplexing Method of Pilot Channel)

FIG. 31 is an exemplary embodiment in a case of assigning differentfrequencies to the data channel transmitting data symbol and the pilotchannel transmitting pilot symbol so as to frequency-multiplex. Asillustrated in FIG. 31, data symbol input from data symbol sequenceinput port and pilot symbol input from pilot symbol sequence input portare multiplied with the spreading codes generated at the respectivespreading code generators 281-1 and 281-2, are multiplied with thescrambling codes generated at the respective scrambling-code generators282-1 and 282-2, and then chip-repeated at the respectivechip-repetition units 284-1 and 284-2 so as to be multiplied bydifferent frequencies (in this case, f1 and f2). Then the symbols arefrequency-multiplexed at the adder 285 for outputting.

As described above, according to the embodiments as illustrated in FIG.29 through FIG. 31, the mobile station multiplexes the pilot channels soas to apply chip repetition to generate the comb tooth-shaped frequencyspectrum. Hereby, an arrangement of transmitting signals from the mobilestations to have a frequency-domain orthogonality is enabled. Moreover,at the base station, a measurement of the received timings at therespective mobile stations using the pilot channel as described above isenabled.

Next, a method of measuring the received timing at the base stationusing the pilot channel as described above is described.

FIG. 32 is a schematic diagram of an exemplary configuration of a basestation which measures received timings of the respective mobilestations by chip-repeated pilot channels. Below an operation of the basestation as described is described, referring to FIG. 32.

In FIG. 32, the base station generates a signal by multiplying the pilotsymbols corresponding to the respective mobile stations generated at thepilot-symbol pattern generator 291 with the spreading code generated atthe spreading-code generator 293, applying chip-repetition at thechip-repetition unit 294, and multiplying the mobile station-specificphase generated at the mobile station-specific phase-sequence generator295. Correlation of such generated signal with the received signal iscomputed at the correlation operator 296 so as to detect the receivedtimings of the mobile station for the respective paths. Herein, thepaths are referred to the respective transmitting signals received atthe base station via different propagation routes. Hereby, a measurementof the received timings of the respective mobile stations using thepilot channel is enabled even in a case of applying chip repetition.

Next, the embodiment in a case of performing the transmission timingcontrol of the respective mobile stations by using the detected receivedtimings of the mobile stations as described above is described.

FIG. 33 is a diagram which describes a transmission timing control inaccordance with the received timings of first paths of the respectivemobile stations.

In FIG. 33, the left portion is a schematic diagram of the receivedtimings of the respective paths for the respective mobile station(herein, mobile station 1, mobile station 2) detected at thereceived-timing detector 297 as illustrated in FIG. 32.

According to the present embodiment, the base station detects for therespective mobile stations paths comprising received power above orequal to a predetermined received power as effective signal power path.Then, based on the detected result, the transmission timing control isperformed such that the first paths of the respective mobile stationsare received at the same timing. For example, as illustrated in theright portion of FIG. 32, the transmitting timings of the respectivemobile stations is controlled so that the received timing of the firstpath of the mobile station 1 and the received timing of the first pathof the mobile station 2 coincide. In other words, the base stationaccording to the present embodiment enables a suppression of the effectof multiple-access interference from other mobile stations according tothe principle of frequency-domain orthogonality with chip repetition byperforming the transmission timing control.

While a case of measuring the received timings from the respectivemobile stations so as to determine the amount of controlling of thetransmission timings from the respective mobile stations based on themeasurement result is described in the embodiment as described above,the wireless transmission system according to the present embodimentcomprises a function of autonomously determining the transmitting timingof the own station. Below an operation of the mobile station asdescribed above is described, referring to FIG. 34.

According to the present embodiment, the mobile station uses the commonpilot signal transmitted to all mobile stations. This common pilotsignal is used for such purposes as the estimation of the received powerat the mobile station, and the estimation of the change in thepropagation channel.

In FIG. 34, in S61, the base station 100 transmits the common pilotsignal to the respective mobile stations 70-1 through 70-n. Therespective mobile stations 70-1 through 70-n receive the common pilotsignal so as to determine the transmitting timing based on that receivedtiming.

In S62, the respective mobile stations 70-1 through 70-n transmit thesignal at the transmitting timing determined as described above, whilethe base station 100 receives the timing-controlled signals from therespective mobile stations 70-1 through 70-n.

The present embodiment, unlike the method of the transmission timingcontrol as illustrated in FIG. 28, enables a simplifying of theconfigurations of the base station and the mobile stations as thecontrolling signal for reporting the transmitting timings fed back tothe respective mobile stations from the base station is not needed. Onthe other hand, the time difference T−D among the mobile stations in thereceived timings, while considered to be larger relative to theembodiment as illustrated in FIG. 28, is considered to be applicable tothe loose transmission control used in the condition in which the cellradius is small.

A Seventh Embodiment

A configuration of a wireless transmission system according to a seventhembodiment is described. The wireless transmission system according tothe seventh embodiment, as in the sixth embodiment, comprises the mobilestations and the base station, applying the transmission timing controlso that the received timings at the respective mobile stations of thepaths having the maximum receiving power coincide. A summary of thefunctions of the mobile stations and the base station according to theseventh embodiment is provided below.

INTERFERENCE SIGNAL FROM OTHER INTERFERENCE MOBILE STATIONS BYMULTI-PATH (MULTIPLE-ACCESS INTERFERENCE) PROPAGATION OF INTERFERENCEFROM INTERFERENCE TRANSMITTING TYPE OF MAXIMUM RECEIVED FROM OTHERSIGNAL INTERFERENCE POWER PATHS PATHS (MULTI-PATH INTERFERENCE) APPLIEDAPPLYING OF STRICT REMOVAL OF MULTI-PATH TECHNOLOGIES TRANSMISSIONINTERFERENCE TIMING CONTROL AT THE BASE STATION (MULTI-PATH INTERFERENCECANCELLER, CHIP EQUALIZER, FREQUENCY-DOMAIN EQUALIZER)

Next, the configuration of the mobile station according to the seventhembodiment is described. FIG. 35 is a functional block diagram whichillustrates a configuration of a mobile station.

In FIG. 35, this mobile station has the configuration with thechip-repetition unit omitted when compared with the mobile stationaccording to the sixth embodiment as illustrated in FIG. 20. Thus,herein such description is omitted.

Moreover, the base station according to the seventh embodiment isconfigured as in FIG. 36, for example, the configuration having thechip-repetition unit omitted as compared with the base station accordingto the sixth embodiment as illustrated in FIG. 21. Thus, herein suchdescription is omitted.

In the wireless transmission system according to the seventh embodiment,the base station performs a strict transmission timing control of therespective mobile stations so that the received timings of the pathscomprising the maximum received power at the respective mobile stationscoincide. Hereby, a reduction of multiple-access interference caused bythe maximum received power paths of other mobile stations is enabled.Moreover, the multiple interference canceller, the chip equalizer, andthe frequency-domain equalizer as illustrated in FIG. 44 through FIG. 46are applied to interference due to the own delay wave caused byinterference from the paths of other mobile stations havingnon-coincident received timings. Hereby, a reduction of the effect ofinterference is enabled.

Next, a specific example of the strict transmission timing controlperformed at the wireless transmission system according to the presentembodiment is described, referring to FIG. 37.

FIG. 37 is a diagram which describes the strict transmission timingcontrol between the mobile station 1 and the mobile station 2. In thepresent embodiment, the strict transmission timing control, asillustrated in FIG. 37, refers to performing the transmission timingcontrol of the mobile station 1 and the mobile station 2 so that thetime difference T−D between the mobile station 1 and the mobile station2 in the received timings of the maximum received power paths becomesalmost 0 (for example, the delay time difference T−D between thereceived symbol i−1 of the mobile station 1 and the received symbol i−2of the mobile station 2 is set to be less than or equal to one-fourth ofthe chip length) so as to coincide the received timings at the basestation. In other words, as the base station performs the transmissiontiming control so that the received timings from the mobile station 1and from the mobile station 2 coincide, a suppression of multiple-accessinterference is enabled by setting the signals having the same receivedtiming from the mobile station 1 and from the mobile station 2orthogonal when the spreading codes applied to the mobile station 1 andthe mobile station 2 are orthogonal codes.

Furthermore, in the wireless transmission system according to thepresent embodiment, the mobile station comprises a function of changingthe scrambling code multiplied to the spreading chip sequence. Themobile station as described above, is configured, for example, as inFIG. 38, having the chip-repetition unit omitted as compared with themobile station according to the sixth embodiment as illustrated in FIG.22. Therefore, herein such description is omitted.

As described above, according to the wireless transmission systemaccording to the seventh embodiment, the mobile station enables anomission of the chip repetition process by applying the stricttransmission timing control.

A Eighth Embodiment

While in the sixth embodiment as described above an exemplary form ofremoving the interfering signal from other mobile stations with acombined use of the chip repetition and the transmission timing controland in the seventh embodiment an exemplary form of removing theinterfering signal from other mobile stations by applying the stricttransmission timing control are described, a wireless transmissionsystem according to the present embodiment comprises a function ofvariably controlling the number of chip repetitions and the spreadingfactor based on the controlling information reported from the basestation in a case of applying chip repetition and transmission timingcontrol in an isolated cell environment.

FIG. 39 is a schematic diagram of an overall configuration of a wirelesstransmission system and a configuration of a mobile station according tothe present embodiment. The controller 58 which is an element specificto the mobile station 50 variably controls the number of chiprepetitions and the spreading factor based on one of the controllinginformation indicating the number of mobile stations (mobile station 200in the present example) simultaneously connected to the base stationtransmitted from the base station 100 as an external apparatus, thecontrolling information indicating the power of interference fromsurrounding cells, and the controlling information indicating thepropagation channel conditions (for example, the number of multi-paths).More specifically, the process is performed according to the flowchartas illustrated in FIG. 40. Besides, it is assumed that the controlleraccording to the present embodiment has already received from the basestation 100 the controlling information indicating the isolated cellenvironment.

Below an operation of the mobile station as described above isdescribed, referring to the flowchart in FIG. 40.

(1) A Case of Indicating the Number of Simultaneously-Accessing Users

Besides, in FIG. 40, the number of users and the number of mobilestations have the same meaning.

In FIG. 40, in S71, the mobile station receives the number of mobilestations within the isolated cell simultaneously-connected to the basestation so as to determine whether that number of mobile stationsexceeds a predetermined threshold value. Moving on to S72 in a case thatthe number of mobile stations exceeds a predetermined threshold value soas to be determined as “having a large number ofsimultaneously-accessing users” (large in S71), the variable controllingwhich increases the number of chip repetitions while decreasing thespreading factor by an amount corresponding to the amount of theincrease as described above is performed. In other words, in an isolatedcell environment, with a large number of simultaneously-accessing users,the number of simultaneously-accessing users is made frequency-domainorthogonal so as to reduce multiple access-interference. Hereby, highspectral usage efficiency is enabled.

On the other hand, moving on to S73 in a case that the number of mobilestations is determined not to exceed a predetermined threshold value(small in S71), the variable controlling which decreases the number ofchip repetition while decreasing the spreading factor by an amountcorresponding to the amount of the decrease as described above isperformed. In other words, in an isolated cell environment, the effectof multiple-access interference becomes relatively small with a smallernumber of simultaneously-accessing users. Therefore, an increase in thespreading factor enables improvement in the interference immunity so asto achieve higher spectral usage efficiency.

(2) A Case in which the Controlling Information from the Base StationIndicates the Power of Interference from the Surrounding Cells.

In FIG. 40, in S81, the mobile station receives the informationindicating the power level of interference from surrounding cells so asto determine whether that power level of interference from surroundingcells exceeds a predetermined threshold value. Moving on to S82 in acase that the power of interference from surrounding cells exceeds apredetermined threshold value (large in S81), the variable controllingwhich decreases the number of chip repetition while increasing thespreading factor by an amount corresponding to the amount of thedecrease as described above is performed. In other words, in an isolatedcell environment, with a larger power of interference from surroundingcells, an increase in the spreading factor increases theneighboring-cell interference immunity. Hereby, higher spectral usageefficiency is enabled.

On the other hand, moving on to S83 in a case that the power ofinterference from surrounding cells is determined not to exceed apredetermined threshold value (small in S81), the variable controllingwhich increases the number of chip repetitions while decreasing thespreading factor by an amount corresponding to the amount of theincrease as described above is enabled. In other words, in an isolatedcell environment, as the effect of intra-cell multiple-accessinterference is predominant with a small power level of interferencefrom surrounding cells, a reduction of multiple-access interference isenabled by setting a number of simultaneously-accessing usersfrequency-domain orthogonal. Hereby, high spectral usage efficiency isenabled.

(3) A Case in which the Controlling Information from the Base StationIndicates the Propagation Channel Conditions (Such as the Number ofMulti-Paths)

In FIG. 40, in S91, the mobile station receives the informationindicating the propagation channel conditions such as the number ofpaths so as to determine whether that number of paths exceeds apredetermined threshold value. Moving on to S92 in a case that thenumber of paths exceeds a predetermined threshold value (large in S91),the variable controlling which decreases the number of chip repetitionswhile increasing the spreading factor by an amount corresponding to theamount of the decrease as described above is performed. In other words,in an isolated cell environment, with a large number of paths, anincrease in the spreading factor enables an obtaining of an increasedmultiple interference immunity.

On the other hand, moving on to S93 in a case that the number of pathsis determined not to exceed a predetermined threshold value (small inS91), the variable controlling which increases the number of chiprepetitions while decreasing the spreading factor by an amountcorresponding to the amount of the increase as described above isperformed. In other words, in an isolated cell environment, as theeffect of multiple-access interference becomes relatively large with asmall number of paths, a reduction of multiple-access interference isenabled by setting a number of simultaneously-accessing usersfrequency-domain orthogonal. Hereby, high spectral usage efficiency isenabled.

In the embodiment as described above, while an exemplary aspect isdescribed in which the respective sets of information indicating thecell environment and of information indicating the number of users, thepower of interference from surrounding cells, and the propagationchannel conditions are individually received at the controller, it mayof course comprise an aspect such that the set of information indicatingthe number of users, the power of interference from surrounding cells,and the propagation channel condition is received when the set ofinformation indicating the cell environment is received.

A Ninth Embodiment

While an exemplary aspect of variably controlling the number of chiprepetitions and the spreading factor at the mobile station in a case ofapplying chip repetition and transmission timing control in an isolatedenvironment is described in the eighth embodiment, in the wirelesstransmission system according to the present embodiment, the mobilestation comprises a function of determining whether a stricttransmission timing control needs to be applied based on the controllinginformation reported from the base station regardless of themulti-cell/isolated cell environments.

FIG. 41 is a schematic diagram of an overall configuration of a wirelesstransmission system and a configuration of a mobile station 60 accordingto the present embodiment. The controller 68 which is an elementspecific to the mobile station 60 determines whether the stricttransmission timing control needs to be executed based on one of thesets of information indicating the number of mobile stations (mobilestation 200 in the present example) simultaneously connected to the basestation transmitted from the base station 100 as the external apparatus,controlling information indicating the power of interference fromsurrounding cells, and controlling information indicating thepropagation channel condition (for example, the number of multi-paths).More specifically, the process is performed according to the flowchartas illustrated in FIG. 42.

(1) A Case in which the Controlling Information from the Base StationIndicates the Number of Simultaneously-Accessing Users

In FIG. 41, in S101, the mobile station receives the number of mobilestations simultaneously-connected to the base station so as to determinewhether that number of mobile stations exceeds a predetermined thresholdvalue. Moving on to S102 in a case that the number of mobile stationsexceeds a predetermined threshold value so as to be determined as“having a large number of simultaneously-accessing users” (large inS101), no strict transmission timing control is performed so that thesame operations as the related-art DS-CDMA are performed. In otherwords, with a large number of users, the effect of performing the stricttransmission timing control diminishes so as not to apply suchcontrolling.

On the other hand, moving on to S103 in a case that the number of mobilestations is determined not to exceed a predetermined threshold value(less in S101), the combined use of the related-art DS-CDMA and thestrict transmission timing control is applied. In other words, with alarge number of users, the effect of performing strict transmissiontiming control enhances so as to apply such controlling.

(2) A Case in which the Controlling Information From the Base StationIndicates the Power of Interference from the Surrounding Cells

In FIG. 41, in S111, the mobile station receives the informationindicating the power level of interference from surrounding cells so asto determine whether that power level of interference from surroundingcells exceeds a predetermined threshold value. Moving on to S112 in acase that the power of interference from surrounding cells exceeds apredetermined threshold value (large in S111), no strict transmissiontiming control is performed so as to perform the related-art DS-CDMAoperations. In other words, with a large power of interference fromsurrounding cells, the effect of performing the strict transmissiontiming control diminishes so as not to apply such controlling.

On the other hand, moving on to S113 in a case that the power ofinterference from surrounding cells is determined in S111 not to exceeda predetermined threshold value (small in S111), the combined use of therelated-art DS-CDMA and the strict transmission timing control isapplied. In other words, with a large power of interference fromsurrounding cells, the effect of performing strict transmission timingcontrol enhances so as to apply such controlling.

(3) A Case in which the Controlling Information From the Base StationIndicates the Propagation Channel Conditions (Such as the Number ofMulti-Paths)

In FIG. 41, in S121, the mobile station receives the informationindicating the propagation channel conditions such as the number ofpaths so as to determine whether that number of paths exceeds apredetermined threshold value. Moving on to S122 in a case that thenumber of paths exceeds a predetermined threshold value (large in S121),no strict transmission timing control is performed so that therelated-art DS-CDMA operations are performed. In other words, with alarge number of paths, the effect of performing the strict transmissiontiming control diminishes so as not to apply such controlling.

On the other hand, moving on to S123 in a case that the number of pathsis determined in S121 not to exceed a predetermined threshold value(less in S121), the combined use of the related-art DS-CDMA and thestrict transmission timing control is applied. In other words, with asmall number of users, the effect of performing strict transmissiontiming control enhances so as to apply such controlling.

In the seventh and the eighth embodiments as described above, whileexemplary aspects are described in which the determination of whetherthe number of users is large or small is performed at the controller ofthe mobile station side, it may comprise an aspect of determining thenumber of users at the base station side so as to report such determinedresult to the mobile station.

As described above, according to the ninth wireless transmission system,the mobile station controls the number of chip repetitions and thespreading factor in accordance with such conditions as the number ofusers, the power of interference from surrounding cells, and thepropagation channel. Hereby, the mobile station enables suppressinginterference to a minimum level so as to improve as a result thespectral usage efficiency.

A Tenth Embodiment

In the wireless transmission system according to the present embodiment,the mobile station comprises a function of switching the operationalmodes based on the cell environment reported from the base station.

(An Operational Mode 1)

Multi-Cell Environment: DS-CDMA

Isolated cell environment: Based on DS-CDMA, the transmitter applieschip repetition and loose transmission timing control, while thereceiver removes the own station multi-path signal by applying themulti-path interference canceller, the chip equalizer, and thefrequency-domain equalizer as illustrated in FIG. 44 through FIG. 46.

(An Operational Mode 2)

Multi-cell environment: Based on DS-CDMA, the transmitter applies stricttransmission timing control and the cell-specific scrambling code.

Isolated cell environment: Based on DS-CDMA, the transmitter applieschip repetition and loose transmission timing control, while thereceiver removes the own station multi-path signal by applying themulti-path interference canceller, the chip equalizer, and thefrequency-domain equalizer as illustrated in FIG. 44 through FIG. 46.

(An Operational Mode 3)

Multi-cell environment: Based on DS-CDMA, the transmitter applies stricttransmission timing control and the cell-specific scrambling code.

Isolated cell environment: Based on DS-CDMA, the transmitter appliesstrict transmission timing control and the cell-specific scramblingcode.

(An Operational Mode 4)

Multi-cell environment: DS-CDMA Isolated cell environment: Based onDS-CDMA, the transmitter applies strict transmission timing control andthe cell-specific scrambling code.

As described above, using the wireless transmission system according tothe tenth embodiment, the mobile station uses the controllinginformation indicating the cell environments as described above toswitch the operational modes based on the cell environment. Hereby, themobile station enables an efficient reduction of interference so as toimprove the spectral usage efficiency.

(A Variation)

While the above embodiments describe the forms of controlling thetransmission timings of the transmitting signals at the mobile stationsso as to set the received timings at the base station coincide among themobile stations, the present invention would not only be limited to theabove embodiments, but also may comprise a variety of variations.

Furthermore in the network environment built temporarily on demand(referred to as an ad-hoc network), in a case of a terminal A and aterminal B having a small propagation delay time difference so as to beenabled to communicate directly, the terminal A receives a transmissiontiming control information from the base station so as to report thetransmission timing control information as described above by thisterminal A communicating with the terminal B. Hereby, the base stationis enabled an omission of the process of transmitting a controllingsignal to a mobile station neighboring a mobile station to be a targetof transmission timing control so as to efficiently utilize the wirelessresources.

The present application is based on Japanese Priority Patent ApplicationNo. 2003-196748 filed Jul. 14, 2003, with the Japanese Patent Office,the entire contents of which are hereby incorporated by reference.

1. A mobile station for wirelessly transmitting to a base station byDS-CDMA a signal which is spread by multiplying a spreading code,comprising: a chip-pattern generating unit which generates one or aplurality of predetermined chip patterns by chip repeating to aspreading chip sequence for a predetermined number of repetitions,thereby generating a signal comprising said predetermined chip pattern;a multiplying unit which multiplies, to the signal comprising saidpredetermined chip pattern, one or a plurality of phases specific tosaid mobile station; a transmission timing control unit which controlstransmitting timings of transmitting signals so that timings ofreceiving at the base station from respective mobile stations coincide;and a timing control switching unit which, when receiving a set ofcontrolling information indicating a cell environment, selects, based onsaid cell environment, one of the low-precision timing control unit anda high-precision transmission control unit which controls transmittingtimings of transmitting signals so that a time difference at the basestation among timings of receiving from the mobile station approacheszero, wherein said transmission timing control unit comprises alow-precision timing control unit which controls said transmittingtimings of the transmitting signals so as to contain time differencesamong the timings of receiving at the base station from the respectivemobile stations.
 2. The mobile station as claimed in claim 1, whereinsaid chip-pattern generating unit, in accordance with a data ratespecified by the mobile station, assigns to the mobile station at leastone of one or a plurality of said chip patterns and one or a pluralityof said phases.
 3. The mobile station as claimed in claim 1, wherein themultiplying unit multiplies, to the signal comprising said predeterminedchip pattern, one or a plurality of phase sequences specific to saidmobile station.
 4. The mobile station as claimed in claim 1, furthercomprising: a variable controlling unit which variably controls at leastone of a spreading factor of said spreading code and the number of chiprepetitions, a scrambling code which is multiplied to the spreading chipsequence, and the phase sequence specific to the mobile station; and anexternal controlling unit which controls, based on a set of controllinginformation, at least one of said spreading factor and number of chiprepetitions, said scrambling code, and the phase sequence specific tothe mobile station.
 5. The mobile station as claimed in claim 1, furthercomprising a multiplexing unit which multiplexes a plurality of channelswhich are multiplied, when chip repeating for the predetermined numberof repetitions, by different spreading codes, said mobile station chiprepeating after said multiplexing.
 6. The mobile station as claimed inclaim 1, wherein said transmission timing control unit comprises apath-based timing control unit which performs, based on first paths, thetransmission timing control so that said first paths are received at thebase station at an identical timing.
 7. The mobile station as claimed inclaim 1, further comprising a guard interval inserting unit whichinserts a guard interval per chip pattern to which the chip repetitionis performed for the predetermined number of repetitions.
 8. The mobilestation as claimed in claim 1, further comprising a chip pattern lengthsetting unit which sets, based on time difference at the base station oftimings of receiving from respective mobile stations, length of chippattern to which the chip repetition is performed for the predeterminednumber of repetitions.
 9. The mobile station as claimed in claim 1,further comprising a pilot-signal transmitting unit which, aftermultiplexing to a transmitting signal a pilot signal having knownamplitude and phase, performs said chip repetition.
 10. A computerreadable medium having stored therein a program for wirelesstransmission and for implementation into a mobile station whichwirelessly transmits to a base station by DS-CDMA a signal which isspread by multiplying a spreading code, said program comprising: achip-pattern generating function of generating a predetermined chippattern by chip repeating to a spreading chip sequence for apredetermined number of repetitions; a multiplying function ofmultiplying, to the signal comprising said predetermined chip pattern, aphase specific to said mobile station; a function of controllingtransmission timings of transmitting signals so as to contain timedifferences at the base station among timings received from the mobilestations to within a predetermined time difference; and a timing controlswitching function of, when receiving a set of controlling informationindicating a cell environment, selecting, based on said cellenvironment, one of the low-precision timing control unit and ahigh-precision transmission control unit which controls transmittingtimings of transmitting signals so that a time difference at the basestation among timings of receiving from the mobile station approacheszero.
 11. A method of wireless transmission, wherein a mobile stationwhich wirelessly transmits to a base station by DS-CDMA a signal whichis spread by multiplying a spreading code, the method comprising: achip-pattern generating step of generating a predetermined chip patternby chip repeating to a spreading chip sequence for a predeterminednumber of repetitions; a multiplying step of multiplying, to a signalcomprising said predetermined chip pattern, a phase specific to saidmobile station; a step of controlling transmission timings oftransmitting signals so as to contain time differences at the basestation among timings received from the mobile stations to within apredetermined time difference; and a timing control switching step of,when receiving a set of controlling information indicating a cellenvironment, selecting, based on said cell environment, one of thelow-precision timing control unit and a high-precision transmissioncontrol unit which controls transmitting timings of transmitting signalsso that a time difference at the base station among timings of receivingfrom the mobile station approaches zero.
 12. The method of wirelesstransmission as claimed in claim 11, wherein said chip-patterngenerating step, in accordance with a data rate desired by the mobilestation, assigns to the mobile station at least one of one or more ofsaid chip patterns and one or more of said phase sequences.
 13. Themethod of wireless transmission as claimed in claim 11, furthercomprising a controlling step performed by said mobile station ofvariably controlling at least one of a spreading factor of saidspreading code and number of chip repetitions, a scrambling code whichis multiplied to the spreading chip sequence, and a phase sequence whichis specific to a mobile station.
 14. The method of wireless transmissionas claimed in claim 11, further comprising the step of controlling,performed by said mobile station which wirelessly transmits to a basestation by DS-CDMA a signal which is spread by multiplying the spreadingcode, transmitting timings of transmitting signals so that timedifference at the base station among timings received from respectivemobile stations approaches zero.
 15. The method of wireless transmissionas claimed in claim 11, the method further comprising: a variablecontrolling step of variably controlling at least one of a spreadingfactor of said spreading code and the number of chip repetitions, ascrambling code which is multiplied to the spreading chip sequence, andthe phase sequence specific to the mobile station; and an externalcontrolling step of controlling, based on a set of controllinginformation, at least one of said spreading factor and number of chiprepetitions, said scrambling code, and the phase sequence specific tothe mobile station.
 16. The method of wireless transmission as claimedin claim 11, further comprising a multiplexing step of multiplexing aplurality of channels which are multiplied, when chip repeating for thepredetermined number of repetitions, by different spreading codes, saidmobile station chip repeating after said multiplexing.
 17. The method ofwireless transmission as claimed in claim 11, further comprising a guardinterval inserting step of inserting a guard interval per chip patternto which a chip is repeated for the predetermined number of repetitions.18. The method of wireless transmission as claimed in claim 11, furthercomprising a chip pattern length setting step of setting, based on timedifference at the base station of timings of receiving from respectivemobile stations, length of chip pattern to which a chip is repeated forthe predetermined number of repetitions.
 19. The method of wirelesstransmission as claimed in claim 11, further comprising a pilot-signaltransmitting step of, after multiplexing to a transmitting signal apilot signal having known amplitude and phase, performing said chiprepetition.